The invention concerns a torsional vibration damper having the following features: an annular damper housing, which delimits a damper chamber; an inertia ring arranged in the damper chamber; a bearing device which supports the inertia ring in the damper housing and which has at least one bearing element with an axial bearing portion and/or a radial bearing portion; and a shear gap between the inertia ring and the damper housing, which shear gap is filled with a viscous fluid.
Torsional vibration dampers of this type serve to damp torsional vibrations on a machine shaft, frequently an engine crankshaft. On the machine shaft, the damper housing of the torsional vibration damper is connected rotationally rigidly to a machine shaft, frequently an engine crankshaft, the torsional vibrations of which are to be damped. The damper housing and the inertia ring follow the mean rotational speed of the machine shaft without slip. Their torsional vibrations however, which are superposed on the even rotation, are initially transmitted only to the damper housing. The inertia ring would rotate uniformly if it were not filled with a viscous fluid, for example a silicon oil, which fills the narrow shear gap to which the damper housing is coupled. This coupling is elastic and thus damped. Consequently, relative rotation angles occur between the damper housing and the inertia ring of e.g. up to ±1 angular degree in time with the exciting shaft vibration. Since the inertia ring can thus rotate slightly in the damper housing chamber relative to the damper housing, usually at least one bearing device is required to support it.
One essential challenge in the design of the bearing device of a torsional vibration damper is to ensure that the inertia ring in the damper chamber is mounted freely movably via the bearing device, and that a collision with the damper chamber or with the damper housing forming the damper chamber is excluded. This is achieved by establishing suitable nominal values and tolerances of the inertia ring, bearing device and damper chamber. Frequently, the installation space for the torsional vibration damper on an engine or internal combustion machine is limited. At the same time, because of the refinement of engines or internal combustion machines, requirements for the function of the rotary vibration damper are rising.
In particular, loosely inserted bearing elements have proved suitable as a bearing device, forming a plain bearing between the inertia ring and damper chamber. Thus it is known to combine a radial strip, slotted at one point on its circumference, with two axial strips—EP 0 423 243—or provide as a bearing device a plurality of axial guide plates as bearing elements—GB 1 307 607.
German Patent Document DE 195 19 261 A1 discloses a torsional vibration damper with a bearing device for guiding an inertia ring in a damper housing, in which as a bearing device at least one bearing element of L-shaped cross section is provided, which is inserted in the damper housing such that a radial bearing portion of the L-shaped bearing element supports the inertia ring radially relative to the damper housing, and an axial bearing portion of the L-shaped bearing element guarantees its axial support and guidance. Shear gaps exist between the inertia ring and the damper housing, and are filled with the viscous fluid. According to variants of this publication, it is provided that two of the L-shaped bearing elements are arranged in the inner or outer circumferential gap of the inertia ring, or one of the L-shaped bearing elements is combined with an axial strip. The L-shaped bearing elements may be configured as circumferentially closed angular rings, or be configured slotted at one place on their circumference.
German Patent Document DE 101 26 477 C1 discloses that the L-shaped bearing elements have a butt joint at one place on their circumference, which is bridged by at least one or more material webs so as to form a circumferentially closed ring. Preferably, these material webs are configured such that on a thermal length extension of the bush, they tear open or deform in an elastic-plastic fashion. According to a further variant of DE 101 26 477 C1, the butt joint is bridged by one or two material webs formed as tear webs, which lie in the alignment of the radial bearing part and/or in the alignment of the axial bearing part. It is also known that the butt joint is bridged by a material web formed as a meandering web, and that the material web is a film web.
The object of the invention is to improve the known bearings for a viscous torsional vibration damper.
The invention achieves this object by providing a viscous torsional vibration damper having the following features: an annular damper housing which delimits a damper chamber; an inertia ring arranged in the damper chamber; a bearing device, which supports the inertia ring in the damper housing and which has at least one bearing element with an axial bearing region and/or a radial bearing region; a shear gap between the inertia ring and the damper housing, and filled with a viscous fluid, wherein several of the axial bearing portions and/or several of the radial bearing portions are circumferentially distributed on the at least one bearing element.
The torsional vibration damper according to the invention obtains a whole range of advantages. Since the axial bearing portions and/or the radial bearing portions no longer extend over the entire circumference, or almost the entire circumference of the bearing element, but only three or more axial and/or radial bearing portions are provided and circumferentially distributed, the space taken up by the respective bearing element in the shear gap is reduced and, correspondingly, additional space is available, which can be filled with the viscous medium and in which a viscous coupling is possible between the inertia ring and the damper housing. This allows the usable shear gap to be maximized and the connection between the inertia ring and damper housing optimized. The axial bearing portions and/or radial bearing portions are those portions in which a plain bearing can be implemented continuously in operation in the axial or radial direction between the damper housing and the inertia ring because of these portions. Preferably, at least three of the axial bearing portions and/or the radial bearing portions are provided, circumferentially distributed on the one or on the two or more bearing elements.
In order to create large regions which are additionally filled with viscous medium, the total circumferential length of the axial and/or radial bearing portions in a preferred embodiment is less than 50%, in particular less than 40%, and particularly preferably less than 30% of the circumference of the entire bearing element.
Preferably, the circumferentially distributed radial bearing portions and axial bearing portions respectively complement each other to form bearing portions of L-shaped cross-section which are provided on the bearing element and circumferentially distributed. Such L-shaped bearing portions ensure that the inertia ring is particularly well centered and guided. Assembly is furthermore very simple in this embodiment, since the bearing element formed in this way can be placed easily in the shear gap before the damper housing, which is usually initially open on one side for installation, is closed after insertion of the bearing element and inertia ring, and filled with the viscous fluid at a filling opening to be closed later.
In a preferred variant, the at least one bearing element furthermore comprises several material webs, each of which connects together two adjacent axial bearing portions and/or two radial bearing portions. These material webs substantially facilitate assembly of the bearing elements. They are preferably dimensioned such that no plain bearing is implemented in operation, or in any case only to a very slight extent. Various variants are conceivable here. Thus it is contemplated that several of the axial bearing portions are connected together by the material webs, and these material webs are configured as axial webs.
Alternatively or optionally however, it is also contemplated that several of the radial bearing portions are connected together by the material webs, and the material webs are configured as radial webs. If only radial or only axial webs are produced, more space is available for the viscous medium. If both radial and axial webs are provided, the stability of the bearing element is improved and its assembly simplified. The material webs also serve to delimit the width of the shear gap, and in some cases act as a short-term emergency bearing if heavy loads occur in these regions during operation.
Here, it is furthermore advantageous if a strip thickness of the bearing element in the region of the material webs is less than a strip thickness in the axial bearing portions and/or in the radial bearing portions, because in this way the space taken up by the bearing element can be reduced further.
To achieve a good support, it is suitable if two of the bearing elements are arranged in the damper chamber. Theoretically, in fact, several bearing elements may be provided. Usually however, two bearing elements are sufficient to support the inertia ring. Thus installation is simple.
It is advantageous if the damper chamber has a substantially rectangular cross-section with inner and outer corner regions. Here, in one variant, two of the bearing elements may be arranged in the outer corner regions of the damper chamber between the damper housing and the inertia ring. This embodiment allows particularly simple installation. This embodiment is advantageous, but not compulsory. Other cross-sections such as C-shapes and similar are possible.
Alternatively, two of the bearing elements may be arranged in the inner corner regions of the damper chamber between the damper housing and the inertia ring.
Finally, one of the bearing elements may be arranged in one of the outer corner regions and another of the bearing elements may be arranged in one of the inner corner regions of the damper chamber between the damper housing and the inertia ring. It is preferred if the bearing elements are arranged in corner regions lying diagonally opposite each other in the damper chamber, since this provides good centering of the inertia ring.
Preferably, the bearing elements of the bearing device are arranged without preload between the damper housing and the inertia ring, in order to guarantee a good support. This is particularly preferred since this ensures good support. A preferred material for the bearing elements of the bearing device is plastic. The viscous fluid is preferably a silicon oil. The bearing elements may however also, in individual cases, be mounted with preload.
In the context of the invention, an embodiment of the bearing device is also possible in which at least one of the bearing elements comprises only axial bearing portions and only axial webs of lower strip thickness connecting these, and/or an embodiment in which one of the bearing elements comprises only radial bearing portions and only radial webs of lower thickness connecting these. These bearing elements are then preferably, but not necessarily, combined with bearing elements in which, in each case circumferentially distributed, the radial bearing portions and the axial bearing portions complement each other to form bearing portions of L-shaped cross-section. Then one of the bearing elements guides the ring preferably in the radial and axial direction, and the other guides the inertia ring only in one of these directions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.